The front wheels of the car are installed with their tops tilted outward or inward. This is called “camber” and is measured in degrees of tilt from the vertical. When the top of a wheel is tilted outward, it is called “positive camber”. Conversely, inward inclination is called “negative camber”. In early automobiles, the wheels were given positive camber in order to improve the durability of the front axle, and to cause the tires to contact the road surface at right angles to prevent uneven tire wear on roads where the center of the road is higher than the edge. In modern automobiles, the suspension and axles are stronger than in the past and road surfaces are flat, so there is less need for positive camber. As a result, tires are being adjusted more toward zero camber (and there are some vehicles with zero camber). In fact, negative camber is now commonly employed in passenger cars to improve cornering performance.

SERVICE HINT:

If the wheels are given excessive positive or negative camber, this causes uneven tire wear. If the wheels are given excessive negative camber, the tires wear quicker on the inside; if the wheels are given excessive positive camber, the tires wear quicker on the outside.

Negative Camber

When a vertical load is applied to a cambered tire, force is generated in the horizontal direction. This force is called “camber thrust” and operates to the inside of the vehicle for negative camber and the outside of the vehicle for positive camber. During cornering, because the vehicle leans to the outside, the tire camber becomes more positive, the camber thrust to the inside of the vehicle is reduced, and cornering force is reduced. The negative camber suppresses the positive camber of the tires during cornering and helps maintain proper cornering force.

Camber During Cornering

When a vehicle turns a corner, the camber thrust on the outside tires acts to reduce the cornering force due to the increase in positive camber. Centrifugal force tilts the turning vehicle due to the action of the suspension springs, changing the camber.

HINT:

Cornering is always accompanied by centrifugal force, which tires to force the vehicle to turn in a larger arc than intended by the driver unless the vehicle can generate a sufficient counterforce – that is, centripetal force – to balance this. This centripetal force is generated by the deformation and side-slipping of the tread that occurs due to friction between the tire and the road surface. This called cornering force.

Camber During Cornering

When a vehicle turns a corner, the camber thrust on the outside tires acts to reduce the cornering force due to the increase in positive camber. Centrifugal force tilts the turning vehicle due to the action of the suspension springs, changing the camber.

HINT:

Cornering is always accompanied by centrifugal force, which tires to force the vehicle to turn in a larger arc than intended by the driver unless the vehicle can generate a sufficient counterforce – that is, centripetal force – to balance this. This centripetal force is generated by the deformation and side-slipping of the tread that occurs due to friction between the tire and the road surface. This called cornering force.

Caster is the forward or backward tilt of the steering axis. Caster is measured in degrees from the steering axis to vertical as viewed from the side. Backward tilt from the vertical line is called “positive caster”, while forward tilt is called “negative caster”. The distance from the intersection of the steering axis centerline with the ground, to the center of the tire-to-road contact area is called “caster trail”. The caster angle affects the straight-line stability and the caster trail affects the wheel recovery after cornering.

SERVICE HINT:

If the wheels are given excessive positive caster, the straight-line stability is improved, but cornering becomes difficult.

Straight-line Stability and Wheel Recovery

Straight-line stability due to caster angle When the steering axis rotates, during cornering, if the wheels have caster angle, the tires are inclined relative to the ground and jack-up torque is generated that attempts to lift the vehicle body as in the figure. This jack-up torque functions as a recovery force that attempts to return the vehicle body to the horizontal and maintains the straight-line stability of the vehicle.

Wheel recovery due to caster trail If the wheels are given caster angle, the contact point of the line extending from the steering axis is forward of the center of tire-road contact. Therefore, since the tires are pulled from the forward direction, the force pulling the tires holds down the force attempting to destabilize the tires and maintains straight-line performance. Also, when the tires face sideways due to steering or disturbance during straight-line travel, side forces (F2 and F’ 2) are generated. These side forces act as rotation forces around the steering axis due to the caster trail and are forces attempting to return the tires to their original positions (recovery force). At this time, if the caster trail is long, for the same magnitude side force, a larger force works to return the steering wheel. Therefore, the longer the caster trail, the greater the straightline performance and recovery force.

Nachlauf and Vorlauf Geometry

In general, the caster angle must be increased in order to increase caster trail. However, even if the caster angle remains the same, the caster trail can be set as desired by offsetting the steering axis to the front or rear from the wheel center. Nachlauf geometry enables caster trail to be increased by offsetting the steering axis to the front from the wheel center. Vorlauf geometry enables caster trail to be decreased by offsetting the steering axis to the rear from the wheel center. In actual vehicles, various settings are made by Nachlauf and Vorlauf geometry in order to match vehicle characteristics.

The axis around which the wheel rotates as it turns to the right or left is called the “steering axis”. This axis is found by drawing an imaginary line between the top of the shock absorber’s upper support bearing and the lower suspension arm ball joint (in the case of strut type suspensions). This line is tilted inward as viewed from the front of the car and is called “steering axis inclination”( S.A.I) or “kingpin angle”. This angle is measured in degrees. Furthermore, the distance “L” from the intersection of the steering axis with the ground to the intersection of the wheel centerline with the ground is called the “offset”, “kingpin offset” or “scrub radius”.

Roles of Steering Axis Inclination

1. Reduction of steering effort Since the wheel turns to the right or left with the steering axis as its center and the offset as the radius, a large offset will generate a great moment around the steering axis due to the rolling resistance of the tire, thus increasing steering effort. This offset can be reduced in order to reduce the steering effort. Either of the following two methods can be used to make the offset small:

(1) Give the tires positive camber

(2) Incline the steering axis.

2. Reduction of kick-back and pulling to one side If the offset is excessively large, the force due to driving or braking generates a moment around the steering axis whose magnitude is proportional to the amount of offset. Also, any road shock applied to a wheel will cause the steering wheel to jerk or kick-back. These phenomena can be improved by reducing the amount of offset. If there is a difference between the left and right steering axis inclination angles, the vehicle will typically pull to the side of the smaller angle (having the larger offset).

3. Improvement straight-line stability The steering axis inclination causes the wheels to automatically return to the straight-ahead position after the completion of turning.

HINT:

In front engine, front-wheel-drive cars, the offset is generally kept small (zero or negative) to prevent the transmission to the steering wheel of shock from the tires generated during braking or by striking an obstruction, and to minimize the moment created around the steering axis by the driving force at the time of quick starting or acceleration.

SERVICE HINT:

If there is a difference between the steering angle on the left and right, there will also be a difference between the moments around the steering axis on the left and right during braking and the braking force will be greater on the side with the smaller steering angle. Also, any difference between the left and right offsets generates a difference in the drive reaction force (torque steer) on the left and right. In either case, a force acts that attempts to turn the vehicle.

Toe is the inclination of the wheel front and rear as seen from above the vehicle. The wheel installation angle is called the toe angle. When the front of the wheels are closer than the rear of the wheels, this is called “toe-in”. The opposite arrangement is called “toe-out”. Roll of toe angle Conventionally, the primary purpose of toe angle has been to cancel out the camber thrust generated when camber is applied. Toe angle therefore prevented the front of the wheel from opening to the out side when toe-in was applied for positive camber. As a result of an increasing use of negative camber and improved performance of the tires and suspension in recent years, however, the need to cancel camber thrust has diminished. Thus, the primary purpose of toe angle has changed to ensuring straight-line stability. When a vehicle rides up on an incline on the road surface, the body tilts to one side. The vehicle feels as if it is about to turn in the direction in which the body is tilted. If the front of each wheel is turned to the inside (toe-in), however, the vehicle will try to move in the direction opposite that in which the body is tilting. As a result, straight-line stability is maintained.

SERVICE HINT:

If toe-in is excessive, the side slip force causes uneven wear of the tires. If toe-out is excessive, it is difficult to secure straight-line stability.

HINT:

Side slip is the total distance that the left and right tires slip to the side while the vehicle is running. Both in the case of toe-in and negative camber, side slip occurs towards the outside.

Frequent inspection and correction of wheel alignment are ordinarily not necessary under normal conditions of use. However, if the tires are worn unevenly, if steering is unstable, or if the suspension has had to be repaired due to an accident, the wheel alignment must be inspected and corrected.

1. General

Wheel alignment covers several items such as camber, caster, steering axis inclination, etc., and each item is closely related to the other items. When inspecting and correcting, it is necessary to consider all items and how they relate to each other.

2. Where to measure and cautions concerning tester handling

Recently a large number of new alignment tester models have come into use. However, note that the high-precision testers may be quite complex, and errors may occur without your being aware of it. Therefore, maintenance of the testers must be performed periodically to assure that they are always reliable. Always measure wheel the alignment with the vehicle parked on a flat, level area. This is necessary because, no matter how accurate the alignment tester is, correct values cannot be obtained if the place where the measurement are to be carried out is not level.

3. Necessity of inspection before measurement of wheel alignment

Before measuring the wheel alignment, each factor that could affect the wheel alignment must be checked and necessary corrections made. Proper execution of this preparatory operation will give the correct values. Standard wheel alignment values are determined by the manufacturer with the vehicle in its “normal” condition. Therefore, when inspecting wheel alignment, it is necessary to have the vehicle as close to its normal condition as possible in which standard values are determined. (See Repair Manual for standard values.) Items to be checked before measurement of wheel alignment area.

• Tire inflation pressure (under standard conditions)
• Markedly uneven wearing of tires or difference in the sizes.
• Tire runout (radial and face)
• Ball joint play due to wear
• Tie rod play due to wear
• Front wheel bearing play due to wear
• Lengths of left and right strut bars
• Difference between left and right wheelbase
• Deformation or wear of steering linkage parts
• Deformation or wear of parts related to front suspension
• Lateral body inclination (chassis ground clearance)

4. Importance of chassis-to-ground clearance

adjustment before alignment measurement

In a vehicle with independent front suspension, wheel alignment factors will vary depending upon the load because of changes in chassis-to-ground clearance. It is therefore necessary to specify the wheel alignment factors for the specified clearance. Unless otherwise specified, refer to the Repair Manual, etc.

5. Road test

After adjusting the front axle, suspension, steering, and/or front wheel alignment, carry out following road test to check the result of the adjustments:

Straight-ahead driving

(1) The steering wheel must be at the correct position

(2) The vehicle should run straight ahead on a flat road.

(3) Excessive steering shimmy or flutter should not occur.

Turning

The steering wheel should turn easily in either direction, and should return quickly and smoothly to the neutral position when released.

Braking

The steering wheel should not pull to either side when the vehicle is broken on a flat, smooth road.

Checking for abnormal noise

No abnormal noise must be heard during the driving test.

6. Measurement results and how to use them

If the measured values deviate from the standard values, it makes the measured values within the standard values by adjusting adjustment mechanisms or replacing parts.

1. Elasticity

If a force (load) is applied to an object made of a material such as rubber, it will create stress (deformation) in that object. When that force is released, the object will return to its original shape. We call this characteristic ÅgelasticityÅh. The springs of a vehicle use the principle of elasticity to cushion the body and occupants of a vehicle from road shock. The steel springs use bending or twisting elasticity.

REFERENCE: Even if an object has elasticity, if the force that is applied to it is excessively large, the elasticity limit will be exceeded, thus preventing the object from completely returning to its original shape. This is referred to as “plasticity”.

2. Spring rate (constant)

The deflection of a spring varies in proportion to the force (load) applied to it. That is, the value obtained by dividing the force (w) by the amount of deflection (a) is constant. This constant value (k) is called the “spring rate” or “spring constant”. A spring with a low spring constant is said to be “soft”, while a spring with a high spring constant is said to be “firm”.

3. Spring oscillation

When the wheels of a vehicle strike a bump, the vehicle’s springs will be rapidly compressed. Since each spring will immediately attempt to return to its original length, in order to release the compressed energy it will extend beyond its original length. Then the spring will respond to the rebound by attempting to return to its original length and will contract to less than its original length. This process, which is called spring oscillation, is repeated many times until the spring eventually returns to its original length. If spring oscillation was left uncontrolled, it would cause not only an uncomfortable ride, but would also lead to handling stability. To prevent this, shock absorbers are also provided.

Toe-angle

To adjust toe-in, change the lengths of the tie rod connecting the steering knuckle arms. 1. In the type in which the tie rod is behind the spindles, increasing the tie rod length increases toe-in. In the type where the tie rod is in front of the spindles, increasing the tie rod length increases toe-out. 2. In the double tie rod type, toe-in adjustment is carried out with the lengths of the left and right tie rod kept identical. If the lengths of the left and right tie rods are different, even correct toe-in adjustment will bring about incorrect turning angle adjustment.

Camber and Caster

Click on the bulb mark or the underlined sentence. The adjustment methods for camber and caster depend on the model. Below are typical methods. Since the toe-in changes if the camber and/or caster are adjusted, the toe-in must always be checked after the camber and/or caster adjustment.

1. Separate camber adjustment On some models, the steering knuckle bolts can be replaced with camber adjusting bolts. Camber bolts have a smaller shank diameter allowing camber adjustment. This type of adjustment is used on strut type suspensions.

2. Separate caster adjustment The caster is adjusted by changing the distance “L” between the lower arm and strut bar by using the nut or spacer of the strut bar. This type of adjustment is used on strut type or double wishbone type suspension, in which the strut bar is located in front of or behind the lower arm.

3. Simultaneous camber and caster adjustment

(1) The eccentric cam type mounting bolt is at the inside end of the lower arm. Turning this bolt moves the center of the lower ball joint to incline and adjusts both the camber and caster. This adjustment method is used on strut type or double wishbone type suspensions.

(2) Turning the eccentric cam type mounting bolts at the front and rear of the lower arm changes the installation angle of the lower arm and changes the position of the lower ball joint. This adjustment method is used on strut type or double wishbone type suspensions.

(3) The upper arm mounting angle, that is, the upper ball joint position, is changed by increasing or decreasing the number and/or thickness of the shims. This adjustment method is used on double wishbone type suspensions.

Example of Camber and Caster

Adjustment

The following is an example of adjusting the Supra JZA80 (1998). (For details, refer to the Repair Manual.)

(1)Measure the camber and caster.

(2) As shown in the chart, read the distance from the marked point to 0 point.

(3) Adjust the front and/or rear adjusting cams according to the values read from the chart.

Turning Radius (Wheel Angle, Turning

Angle)

The type with a knuckle stopper bolt can be adjusted, but the type without this bolt cannot be adjusted.

HINT:

In the case of rack-and-pinion steering gear, the wheel angle is typically determined by the point at which the steering rack end makes contact with the steering rack housing. Consequently, there is usually no knuckle bolt. If the lengths of the left and right tie rod ends are different,

Rear Wheel Alignment

Rear wheel alignment of an independent rear suspension is accomplished by adjusting the camber and toe angle. The method of adjusting the camber and toe angle differs depending on the type of suspension. Some models have no mechanism for adjusting the camber.

The vehicle must have proper straightline performance for stable driving, cornering performance for driving around curves, recovery force for returning to the straight-line condition, the capacity to soften the shock transmitted to the suspension when the tires are impacted, etc. Therefore, the wheels of a vehicle are mounted at specific angles to the ground and specific suspensions for each purpose. This is called wheel alignment. The wheel alignment has the following five factors:

• Camber
• Caster
• Steering axis inclination (kingpin inclination)
• Toe (toe-angle, toe-in and toe-out)
• Turning radius (wheel angle, turning angle) If even one of these elements is incorrect, the following problems can occur:
• Difficult steering
• Poor steering stability
• Poor recovery on curves
• Shortened tire life

1. Switches

(1) Damping mode select switch This switch can change the shock absorber damping force. The switch positions and details of the settings depend on the model, but switching from COMFORT (or NORM) to SPORT changes the damping force from soft to firm.

Construction

(1) Damping mode select switch

(2)Height control switch

This changes the vehicle height setting. The switch positions and details of the settings depend on the model, but switching from NORM (or LOW) to HIGH changes the vehicle height from low to high.

(3) Damping mode indicator light and vehicle height indicator light The damping mode indicator light lights by mode selection with the damping mode select switch. The vehicle height indicator light is lit up by mode selection with the height control switch. Also, these indicator lights are blinking during system malfunction. The contents of these indicator lights depend on the model.

(4) Stop light switch

(5) Door courtesy switch

2. Sensors

(1) Steering angle sensor The steering angle sensor is fitted to the turn signal switch assembly and detects the steering direction and angle. The sensor contains 3 photo interrupters with phases, and a slotted disc interrupts the light to turn the phototransistor ON and OFF to detect the steering direction and angle.

Steering angle sensor

Height control sensor

Deceleration sensor

(2) Height control sensor A height control sensor is incorporated in each wheel. This sensor converts change in the height of the vehicle into change in the control link rotation angle. Then, the result is detected in the form of voltage change. When the vehicle becomes higher, the signal voltage becomes higher; when the vehicle becomes lower, the signal voltage falls.

(3) Deceleration sensor The front acceleration sensor is integrated with the front height control sensor and the rear acceleration is installed in the luggage compartment. The acceleration sensors convert deformation of the piezoelectric ceramic disc into an electrical signal and the vehicle vertical direction acceleration is detected. When upward acceleration of the vehicle, that is upward force, is received, the signal voltage rises; when downward force is received, the signal voltage falls.

3. ECU/Actuators

(1) EMS/Air suspension ECU The EMS/air suspension ECU serves the role of processing the signals received from the sensors and the selector switch and converting them into the signals for driving the actuators and valves.

(2) Suspension control actuator The suspension control actuator is located at the top of each shock absorber/pneumatic cylinder. It changes the shock absorber damping force by the output shaft rotating the shock absorber rotary valve. The rotary valve (output shaft) rotation angle is controlled by signals from the EMS/air suspension ECU.

(3) Pneumatic cylinder with shock absorber/shock absorber The pneumatic cylinder consists of a variable damping force shock absorber containing low-pressure nitrogen gas and an air chamber with a large compressed air capacity in order to realize excellent riding comfort. To switch the shock absorber’s damping force, a hard damping valve and a soft damping valve have been provided. The damping force is varied by the rotary valve, which changes the ratio of oil that passes through the valve

(4) Compressor and dryer assembly The compressor and dryer assembly has an integral construction with the compressor and motor to make the compressed air necessary for raising the vehicle height, the dryer to eliminate the moisture in the compressed air made by the compressor, and the exhaust valve to drain the compressed air to the atmosphere from the pneumatic cylinders.

(5) Height control valve The height control valves control the flow of compressed air to and from the pneumatic cylinders depending on signals from the air suspension ECU. Two height control valves are provided, one for the front and the other for the rear.

The suspension improves the riding comfort and driving performance of the vehicle. EMS (Electronically-Modulated Suspension) and air suspension electronically control the damping force of the shock absorbers and air springs to further improve riding comfort and driving performance.

EMS

EMS is an abbreviation which stands for “Electronically- Modulated Suspension”. The size of the shock absorber orifice is changed so that the amount of oil flow is adjusted, causing the damping force to vary. The damping force is automatically controlled by the EMS ECU (electronic control unit) according to the selector switch condition and the driving condition. This ensures increased driving comfort and provided excellent driving stability. Diagnostic functions and a fail-safe function are also provided.

Air Suspension

The air suspension uses an ECU to electronically control the suspension which uses air springs that utilize the elasticity of compressed air. There are also models that combine air suspension with EMS. The air suspension has the following features.

• The damping force can be changed.
• The spring rate and vehicle height can be changed by adjusting the air volume.
• Diagnostic functions and a fail-safe function are also provided.

Characteristics

The EMS & air suspension have the following features.

1. Mode change

(1) Damping mode select The damping force of the shock absorber can be changed from soft to firm.

(2) Height control (Air suspension only) The vehicle height setting can be changed from low to high. There are indicator lights that show the status for both the damping mode and the height control.

2. Damping force and spring rate control

(1) Anti-squat control

Changes damping force to firmer. This suppresses squatting during acceleration, thus minimizing changes in vehicle posture.

(2) Anti-roll control

Changes damping force to firmer. This suppresses rolling, thus minimizing changes in vehicle posture, providing excellent controllability.

(3) Anti-dive control

Changes damping force to firmer. This suppresses nose-diving during braking, thus minimizing changes in vehicle posture.

(4) High-speed control (normal mode only)

Changes damping force to firmer. This control provides the excellent driving stability and controllability at high speed.

(5) Shift-squat control (A/T vehicles only)

This limits the amount of rear-end squat when a vehicle with an automatic transmission first starts out. When the transmission shifted from the “N” or “P” range, the damping force is set to firm.

(6) Semi-active control

Smoothly changes the damping force to a target value in accordance with the changes in the road surface or driving conditions. Thus, excellent ride comfort has been realized while ensuring a high level of vibration damping performance.

Sky-hook EMS:

Putting the vehicle in the sky-hook state constantly achieves a stable vehicle attitude in relation to the change of the road condition. In sky-hook EMS using this theory, the up and down motion of the body is sensed and a computer finely controls and adjusts the movement of the shock absorbers. This system greatly improves ride comfort and driving stability. In the latest models, such as the LS430, the semiactive control of the damping force control has been changed from sky-hook control to non-linear H_ control in order to effect even more fine control. As a result, excellent ride comfort has been realized.

3. Vehicle height control

(1) Auto-leveling control

Maintain vehicle height at a constant level regardless of the passenger and luggage weights. Operation of the height control switch changes the target vehicle height to “normal” or “high” level.

(2) High-speed control

Controls vehicle height to a lower side than the height selected by the height control switch (to lower position if “normal” is selected or to normal if “high” is selected) when the vehicle is driven at a prescribed speed or higher. This provides aerodynamics and excellent stability at high speed.

(3) Ignition switch-off control

Lowers vehicle height to target height when vehicle height becomes higher than target height due to a reduction in weight of passengers or luggage after ignition switch is turned off. This improves vehicle posture during parking.

HINT:

Method to cancel the vehicle height control:

Before jacking up the vehicle or raising it on a hoist, make sure that the ignition switch is turned OFF.

If the vehicle must be raised with its engine running, jump terminals TD and EI of the TDCL or OPB and CG of the DLC3 (Data Link Connector 3) to stop the vehicle height control operation of the air suspension ECU.

For the vehicle with the height control ON/OFF switch, the switch is turned OFF.